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Mr. Brooke on the 



[Jan. 



Article II. 



On the Crystalline Forms of Artificial Salts. 

 By H.J.Brooke, Esq. FRS. 



{Continued from vol. vi. p. 439.) 



It has been suggested to me that these descriptions of the 

 crystalline forms of the salts ought to be accompanied by an 

 exact analysis of each, in order to avoid the chance of misnomer, 

 and to render the description of each complete. It certainly 

 would be more satisfactory to know the composition of the salts 

 described. This cannot, however, be conveniently given with 

 the figures, but I have stated generally the authority upon 

 which they have been severally named, and they may at any 

 time be compared with the forms of ascertained compounds. 



Sulphate of Potash. 



The primary form of this salt was, I believe, first determined 

 by Mr. Levy to be a right rhombic prism, and described in 

 ISo. 30 of the Royal Institution Journal; but probably from not 

 possessing sufficiently explanatory crystals, Mr. L. has not 

 pointed out the relation of its primary form to the bi-pyramidal 

 figure under which it generally occurs. 



I have been enabled to do this in a 

 very satisfactory manner by means of a 

 compound crystal which 1 have obtained Fig. I. 



from the solution of a portion of this salt 

 in distilled water. 



Fig 1. is a single modified crystal. 



M on M' 120° 30' 



MonA 120 45 



M on e 146 22 



Aon c 146 10 



tone' 131 12 



Fig. 2 is the compound crystal, which 

 consists of three single crystals, so united 

 that their upper edges meet at angles of 

 120°, and consequently their planes of 

 junction incline to each other at the same 

 angle. Hence 



MonM" 119° 30' 



eone" 130 24 



Fig. 2. 



